This invention relates to alpha-fluoroalkyl compounds related to tetrabenazine and dihydrotetrabenazine and intermediates useful in the preparation of such alpha-fluoroalkyl compounds.
Since first reported on in 1957 (Pletscher, A. (1957) Release of 5-hydroxytryptamine by benzoquinolizine derivatives with sedative action, Science 126, 507), tetrabenazine and structurally related compounds have been widely investigated, and a number of TBZ compounds and derivatives of tetrabenazine have shown promise in the treatment of a variety of conditions affecting human health. For example, dihydrotetrabenazine has been identified as an agent for the treatment of schizophrenia and other psychoses (See for example WO 2007017654 A1), and tetrabenazine has shown promise as an agent in the treatment of Huntington's disease (Neurology (2006), 66(3), 366-372). Although most preparations used in biological studies of tetrabenazine and its derivatives have been carried out on racemates, in at least one instance the biological activity exhibited by enantiomers tested separately was highly differentiated (See Koeppe, R. A. et al. (1999) Assessment of extrastriatal vesicular monoamine transporter binding site density using stereoisomers of [11C] dihydrotetrabenazine, J Cereb Blood Flow Metab 19, 1376-1384).
More recently, derivatives of 9-desmethyl(±)-dihydrotetrabenazine incorporating a fluorine-18 atom have been shown to be useful as PET imaging agents, Nuclear Medicine and Biology 33 (2006) 685-694. See also Nuclear Medicine and Biology 34 (2007) 239-246; and Nuclear Medicine and Biology 34 (2007) 233-237.
The present invention provides both a new class of fluorinated dihydrotetrabenazine derivatives and fluorinated dihydrotetrabenazine analogs, and discloses efficient synthetic methodology which may be used to prepare such compounds in enantiomerically enriched or racemic forms. The alpha-fluoroalkyl dihydrotetrabenazine compounds provided by the present invention are useful as PET imaging agents, probes for the development of PET imaging agents, and therapeutic agents. In addition, the present invention provides novel synthetic intermediate compositions which may be used to prepare either or both enantiomers of the subject dihydrotetrabenazine derivatives and dihydrotetrabenazine analogs.